Due to the high level of crystallinity of polyphenylene sulfide (PPS), monofilaments thereof tend to be brittle and are difficult to work with. In particular, the knot strength, the loop strength, and the fatigue resistance of 100% PPS monofilaments are low and, thus, result in problems during the processing of the monofilaments, especially when a monofilament is woven into fabric. For example, when a 100% PPS monofilament is removed from the quill during weaving, twists and loops form which, when tightened, kink and result in filament breaks.
Nevertheless, PPS, because of its performance at elevated temperatures and its good chemical resistance, is believed to be a good candidate for fiber applications. In U.S. Pat. No. 3,895,091, a process for producing 100% PPS filaments is disclosed. High modulus, high melting, non-burning PPS fibers with good corrosion resistance properties were obtained.
PPS has been blended with such materials as polytetrafluoroethylene (PTFE), polyether ether ketone (PEEK), polyetherimide (PEI), low density polyethylene (LDPE), and certain other fluorocarbon polymers See U.S. Pat. Nos. 3,487,454; 4,421,588; 4,455,410; 4,493,917; and 4,544,700.
In U.S. Pat. No. 3,487,454, the moldability and extrudability of PPS resin is improved by the addition of polyfluorocarbon polymers to the PPS resin. The only polyfluorocarbon polymer disclosed is polytetrafluoroethylene (PTFE) resin. The PTFE resin is added in the range of 0.5 to 10 percent by weight of the PPS.
In U.S. Pat. No. 4,421,588, PPS is blended with polyether ether ketone (PEEK) to produce a plastic alloy suitable for use as a moldable bearing material, having a high fatigue strength and improved thermostability.
In U.S. Pat. No. 4,455,410, 1-99% by weight PPS is mixed with a 99-1% by weight polyetherimide (PEI) for the purpose of obtaining a molding grade material with good flexible strength and better mechanical properties than PPS alone.
In U.S. Pat. No. 4,493,917, chemical resistant fluorocarbon polymers are mixed with heat-stable polymers, such as PPS, in order to improve the mechanical properties of the fluorocarbon polymer used to make frames for electrochemical reaction cells. The fluorocarbon polymer forms an anti-corrosion barrier around the structural matrix formed by the PPS. The fluorocarbon polymers may be chosen from: polytetrafluoroethylene (PTFE) resins, such as "Soreflon 71" from PCUK Company; or dispersions of fusible, fluorinated copolymers, such as polyfluoroethylene, perfluorinated ethylene-propylene copolymer; or perfluoroalkoxy resin. The process for preparing the frames required two steps: preparing the blend by extrusion, and then producing the frame by molding.
In U.S. Pat. No. 4,544,700, PPS, when used as a matrix binder in carbon fiber or glass fiber composites, is mixed with a low density polyethylene (LDPE). The resulting composite has a reduced tendency to develop internal cracks within thick-walled parts.
Specific efforts directed at forming PPS into monofilaments, that may be subsequently woven into fabrics which are suitable for the harsh thermal and chemical environments encountered in the papermaking process, have investigated various additives that can improve PPS monofilaments. The additives are used, in part, to reduce the brittleness of PPS monofilaments by improving the loop strength, the knot strength, and the fatigue resistance of the monofilament. See U.S. Pat. Nos 4,610,916; 4,748,077; and 4,801,492.
In U.S. Pat. No. 4,610,916, PPS is mixed with copolymers comprising olefins and halogenated monomers for the purpose of reducing PPS monofilament brittleness. Reduced brittleness results in better loop strength, knot strength and abrasion resistance, however, the tensile strength is reduced somewhat. An exemplary copolymer is polyethylene-tetrafluoroethylene. Exemplary halogenated monomers include tetrafluoroethylene, fluorinated ethylene-propylene, chlorotrifluoroethylene, vinylidene fluoride, hexafluoropropylene, but specifically excluded are vinyl chloride, vinyl fluoride, and trifluorostyrene.
In U.S. Pat. Nos. 4,748,077 and 4,801,492, PPS is mixed with melt-extrudable polymers to form novel monofilaments. The melt-extrudable polymers are divided into four categories: (1) non-halogenated polymers and copolymers of olefins; (2) halogenated homopolymers; (3) ionomer resins; and (4) aromatic aliphatic polyamides and aliphatic aromatic polyamides. See U.S. Pat. No. 4,748,077, column 4, line 26--column 6, line 53 which is incorporated herein by reference. The second category, halogenated homopolymers are particularly relevant to the instant invention. Halogenated homopolymers, as defined, have from 2 to 8 carbon atoms and contain fluorine or chlorine or both as the halogen. Exemplary homopolymers include polyvinylidene fluoride, polyvinyl fluoride, polyvinyl chloride, polychlorotrifluoroethylene, as well as polymers of hexafluoropropylene.
In view of the above, there is a continuing need to improve the PPS resin blends used to manufacture PPS monofilaments.